Upcycling Automotive Recyclate and Miscanthus Derived-Biocarbon for Sustainable Composite in Automotive Applications

Abstract

We develop impact-toughened, sustainable composites from recycled polypropylene (r-PP) derived from waste automotive parts, pyrolyzed miscanthus biomass (biocarbon) as a filler, and maleic anhydride-grafted polypropylene (MAPP) as a compatibilizer. This work uniquely valorizes two waste streams simultaneously consisting of post-consumer automotive rPP and miscanthus-derived biocarbon, a co-product of biomass pyrolysis into a single upcycled composite. rPP was blended with an ethylene-octene copolymer (EOC) to improve impact resistance. Biocarbon and MAPP were added to recover stiffness and enhance thermal/dimensional stability. The addition of EOC to the biocarbon-filled composite improved notched Izod impact strength by 21%. Adding 20 wt% biocarbon increased the flexural modulus by 10%, lowered the coefficient of linear thermal expansion (CLTE) by ~11% in the flow direction and ~17% in the normal direction, and increased the heat deflection temperature by 18%. Density remains ≤ 1 g cm⁻³, with a total sustainable content of 75%. A simple micromechanical model was used to extract a reinforcement efficiency factor r, which increased from -0.3 (uncompatibilized BioC composite) to 0.33 with MAPP, indicating significantly improved filler dispersion and interfacial stress transfer. Biocarbon and MAPP synergistically enhance interfacial stress transfer and restrict chain mobility, thereby enabling the formation of tougher, stiffer, and thermally stable rPP-based composite materials with increased sustainability, using recycled polymers and bio-derived fillers for non-structural automotive components.